(1) Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to an active-matrix type liquid crystal display device.
(2) Background Art
In an active-matrix type liquid crystal display device, on a liquid-crystal-side surface of one substrate out of respective substrates which are arranged to face each other in an opposed manner while sandwiching a liquid crystal therebetween, respective regions which are surrounded by gate signal lines which are extended in the x direction and are arranged in the y direction in parallel and drain signal lines which are extended in the y direction and are arranged in the x direction in parallel are formed as pixel regions. Each pixel region includes an active element which is operated in response to scanning signals from the gate signal line, a pixel electrode to which video signals from the drain signal line are supplied via the active element, and a capacity which is generated between the active element and the pixel electrode.
The liquid crystal display device having such a constitution realizes an image display by performing writing for a fixed time with the use of the active element and subsequent holding for a fixed time.
As holding methods, a Cadd (added capacity) method which generates a capacity between the gate signal line and the pixel electrode and Cstg (holding capacity) method which generates a capacity between a holding capacity signal line and the pixel electrode have been known.
Although the numerical aperture is lowered in the Cstg method since the method requires the holding capacity signal lines, the method can obtain a relatively high quality image since the holding potential can be made stable.
Further, as a liquid crystal display device using the Cstg method, a so-called lateral electric field type liquid crystal display device has been known. This type of liquid crystal display device is constituted such that on a substrate side on which pixel electrodes are formed, reference electrodes which generate an electric field between the pixel electrodes and the reference electrodes are mounted. Holding capacities are formed by superposing pixel electrodes on reference signal lines which supply reference signals to the reference electrodes via insulation films.
As liquid crystal display devices which can realize the broadening of a viewing angle of the display of the liquid crystal display device, liquid crystal display devices which adopt this Cstg method have been commercialized.
On the other hand, to ensure a uniform gap (cell gap) between respective substrates which are arranged to face each other in an opposed manner while sandwiching a liquid crystal therebetween, a constitution which disperses polymer stationary beads in the inside of the liquid crystal or a constitution which provides support columns made of organic material to one substrate surface by a selective etching with the use of a photolithography technique has been known.
Although the leaking of light is generated in the periphery of the beads or the support columns, the technique which arranges the support columns in the inside of the screen can preliminarily set their positions and hence, the technique can realize the enhancement of the contrast ratio compared to the technique which uses the dispersion of beads.
Further, as a mounting method of drivers (semiconductor chips) which supply signals to the active elements, a TCP method and a FCA (also referred to as “COG”) method have been known.
The TCP method has a feature that the method can manufacture the liquid crystal display devices more easily than the FCP method and can enhance the yield. On the other hand, the FCP method can decrease the number of wiring which are pulled out to the outside so that the method is suitable for a high definition.